Distribution of intelligence



21 192 June 7- H. A. AFFEL DISTRIBUTION OF INTELLIGENCE Original FiledFeb. 25. 1922 @sheets-sheet 1 -Q Y A A I I l I I I., d

INVENT'OR JM ,W24

ATTORNEY U11 DQ I l l l l D, I we :El

June 21, 1927.

H. A'. AFFEL DISTRIBUTION 0F INTELLIGENCE Original Filed Feb. 25. 1922 n2 sheets-sheet 2 @hy/law@ Line INVENTORV ATTORNEY nennen' a. arret, er

aanstaan ana rename at, naa,

'llhis invention relates to signaling systenis and more particularly tosystems for the distribution oi news, `amilseinent and the like. j

The field ot communication may be con sidered to be broadly .dividedinto two classes, first, those communications destined. betweenparticular or individual points,`

i and` second', broadcast communications in io vvolving generalYdisseinination ot intelli genre amonga large number ot individuals orpoints, and which are not conlldential. 'llie telephone art has beendeveloped along lines ot communication :telling into the iirstclassabove mentioned. itt is the purpose ot the present invention,however, to provide a system whereby the telephone art may be applied tocommunications et the second class. i

ln carrying out the invention it is proposed to organize a system inwhich intellin gence such asmusic and news may be tran niitted -troinpoints at which the intelli gence originates to a common distributingpoint. At the common distributing point the signaling currentsrepresenting the various types of intelligence will be translated intocarrier frequencies by modulation and by superposing the translatedfrequencies upon a common transmission network, the several types ofintelligence may be simultaneously transmitted to a plurality ofreceiving` stations. By employing carrier currents having a sufficientlyhigh frequency with respect-to the widthv of the band necessary toaccurately reproduce the low frequency signaling currents, distortionresulting Jfrom ordinary telephonie transmissions will be practicallyeliminated. Another ad- 4'ant-age inherent in the use of carriercurrents resides in the fact that by multiplexing the circuitsdill'erent carrier Jfrequencies may be assigned to the transmission of anumber ot different forms of amusement and news which are. transmittedsimultaneously over the system, so that the subscribers will be enabledto choose the particular form of amusement or news desired.

For the transmisfion of the carrier requencies 'from the centraldistributing point to the siibsci'il' eis stations,4 existing net workssuch as telephone circuits or power circuits leading to the premises otthe individual subscribers may be utilized. ln ac cordance with thepresent invention the unbe amplified to practically any HGTELATJGENGE.

No. 539mm. Renewed nebrnary 9 modulated carrier frequencies assigned ltothe several channels will be amplilied and transmitted over 'the powei`circuit to the substations where they may be used to beat with the sidebands to reproduce the original signal. rlhe side bands, on tbe otherhand, being currents of relatively small amplitude, may be transmittedover telephone lines ex- 'tending1 to the subscribers stations.

At the subscribers station a'vacuum tube detector may be employed fordetecting the signaling currents from the side bands by beating themwith the proper carrier trequencies. The detectors may be supplied withoperating currents from the power cir cuit. ln order to select anydesired type oi intelligence, asimple tuned circuit may be arranged toselect any one ot several tretiti queiicies by means of a suitableswitch so that by this simple means the carrier frequency correspondingto the desired type oit' transmission may be selected from the powercircuit and applied to the detector, together with the side bandscorresponding to all of the different types of transmission. Only theside band correspondingr to the selected carrier will produceanintelligible and audible signal9 as the frequencies resulting frombeating the other side bands with the carrier will be abovea-udibility.. A loud speaker will be provided to be operated by thedetested signaling currents.

This method ot transmitting the unmodu lated carrier frequencies overone circuit, and the side bands over another circuit, has severaladvantages. For example, by transmitting the carrier frequencies overthe power circuit the carrier frequencies may desired degree, as hasalready been pointed out. This is for the reason that the power circuitsare not only excellent conductors because of the large quantities ofcopper employed, but for the further reason that the question ofinterference from crosst-alk in adjacent circuits need not be consideredto the same extent as in the case of telephone circuits. Anotheradvantage resides in the tact that by transmitting the unmodu latedcarrier frequencies' over a circuit separate trom that carrying the sidebands, a

vvery simple selective device may be used to select the desired carrier,and no selection with respect to the side bands becomes necessary 'llhisis an important testare, since to panying drawings, Figure 1 ofwhichshows the apparatus employed at the central distributing station,and Figs. 2 and 3 of which illust-rate two different types of apparatus.

` which may be employed at the subscribers station.

Referring to Fig. 1, S1, S2 and S, represent three different points'orsources of intelligence, one being, for example, a classical concert,another a popular concert, or lecture, and the third a point at which anews bulletinl or other information is recited. Transmitters areprovided vat each of these points and the transmitters are connected bymeans of lines L1, L2 and L3 to'the main distributing station, at whichmodulators M1, M, and M3 are provided. The modulators, as illustrated,are duplex vacuum tube modulators of the type illustrated in CarsonPatent 1,343,308, of June 15, 1920, and are arranged to suppress thecarrier. The three modulators M1, M2 and M3 have their filamentssupplied with heating current from a power circuit. PL, over whichalternating power currents' from a generator G are transmitted. Theconnection 10, between the filaments of the modulators and the powercircuit PL, includes a choke coil 11 to keep the carrier frequencies,which are transmitted over the power circuit in a manner describedhereinafter, from being transmitted to the filaments. The plate voltagesfor the modulators arey also obtained from the power circuit PL througha branch 12, which includes a motor generator or a rectifyingarrangement schematically indicated at 13. Any well known type of motorgenerator or rectifier may be used,

' the purpose of this portion of the apparatus being to change thealternating power currents into direct currents to energize thefilament-plate circuits of the tubes. In order to smooth out rectifiedcurrents, a simple form of low-pass filter comprising shuntinductanceand series capacity may be included in the branch circuitsleading from the circuit 12 to the plate connections of each of themodulators, as indicated at 14, 15 and 1G.

The modulating signal'frequencies from I the sources S1, S2 andS3 areimpressed upon the modulators from the lines L1, L2 and L3 throughtransformers 17, 18 and 19, in such a manner as to be serially appliedwith respect to the grids of the two tubes. The

carrier frequencies are supplied to the tubes in parallel with respectto the two grids through connections indicated at 20, 2l and 22. Byconnecting the circuits in this manner the uninodulated carriercomponent is suppressed in the output circuits of the modulators andonly the side bands will be transmitted through the output transformers23, 2-1 and 25. Band filters 2G, 2T and 28 are included between thesetransformers and the common circuit 29, leading to the telephone lineTL. These band filters may be of the well known Campbell type and aredesigned to transmit one side band only for each channel, the other sideband beingr suppressed by the filter. The `side bands transmitted fromthe three channels will, ot' course, lie in diiiercnt frequency ranges,the frequency range being determined by. the lfrequency of the carriersupplied to the modulator of each channel. The telephone line TL may, ofcourse, be used for ordinary telephonie communication and in order thatit may be connected withJ other lines,

it is terminated in a jack J, as indicated, and a low-pass filter 30 isconnected in the line between the jack J and the connection ofthecircuit 29 to prevent the frequencies in the modulated side bands frombeing transmitted over the jack to some other telephone line which maybe lconnected to the line TL.

The carrier frequencies to be supplied to the modulators may be obtainedfrom the basic frequency transmitted by the generator G over the powercircuit PL, or they may be obtained from a special fundamental carriersource G', depending upon which way the switch 31 is thrown. The switch31 is included in a circuit leading to a harmonic generatorschematically indicated at 32. This harmonic generator may be of anywell known type, such, for example, as a vacuum tube whose circuit isarranged to distort the fundamental'frequency applied toits inputcircuit, thereby producing harmonics in the output circuit in a wellknown manner. The particular harmonics appearing in the output circuit33 of the harmonic generator which it is desired to use as carriers maybe amplified by amplifiers 34, 35 and 36, and selected by means ofsharply tuned circuits 37, 38 and 39 from the undesired harmonics. Theamplifiers 34, 35 and 36 may be of any well known type such, forexample, as vacuum tube amplifiers.

The harmonics selected by the timed circuits 31', 3S and 39 aresuperposed as immodulated carriers upon a common circuit 40 which isconnected through a high-pass filter 41 to the power circuit PL. Thefilter Al1 permits of transmitting the amplified carriers from thecircuit 40 to the power circuit, while preventing the low frequenciesfrom the source G from being transmitted into the circuit 40. A low-passfilter 42 may be included in the power circuit as indicated, to preventthe carrier frequencies llU wearer from reacting on the generator GQ Thethree carrier frequencies which have beenl selected and superposed upon4the circuit 4U may 'hey selectively transmitted over the cir-v cies,however, being transmitted over the power circuit lPL. 'llhe `carrierfrequencies are not, however, transmitted over the line lTL for thereason that they are suppressed by the modulators, as already stated,and only one side band is transmitted over the telephone line for eachchannel.

At the subscribers station, the apparatus may be arranged as shown inFig. The power circuit PL leads through the transformer 46, cut-out box47 and meter'45 toa load 49, which may be a series of electric lights orother current-consuming devices. The transformer 46 will ordinarily bedesigned to transmit only the power frequencies supplied by thegenerator Gr, but by arranging by-pass condeusers 5G and 5l about thetransformer, the carrier frequencies may be passed through thetransformer and into the tuned circuit 52.

'llhe detecting apparatus D, at the subscrihers station, comprises aduplex vacuum tube arrangement of the general type illustrated in CarsonPatent 1,343,308, of dune l5, 1920, and the filament circuit of thedetector D is energized from the power circuit PL over a branch 53,including choke coils 54 for the purpose of preventing the carrierfrequencies from entering the filament circuit. In some instances, theinductance of the meter 48 will be suliicient to choke out the carrierfrequencies. The late voltage for the detector isV also supplied fromthe power circuit through the branch 53 and a motor generator orrectifier 54', this ap aratus being similar to the corresponding geviceat the main distributing station. The connection from the motorgenerator or rec.- tifier 54 to vthe plate-filament circuit of thedetector D must be shunted by a condenser 55 to form a path of lowimedance for the high frequency currents. X loud speaker 56 is included inthe output circuit of the detector and a Simple low-pass filterarrangement 57, 58 is included in circuit with the windings of the loudspeaker 56 to permit `the transmission 'of the detected low frequencysignaling currents to the loud speaker, while preventing the highfrequencies from passing into the loud speaker circuit. The highfrequencies will be shunted from the loud speaker by passing through thecondenser 55 and the first shunt condenser of the filters 57 and 58.

ing station 'may be passed througha high-y y pass filter 59 and atransformer 60, to be im pressed upon the input circuit ot the de tectorl) serially with respect to tlie grids ol thetwo tubes ot' the detector.liy ,means of a switch (il, the tuned circuit 52 may be set for thecarrier frequency corresponding to any desired side band and theselected carrier frequency transmitted, over a circuit 52 so as to beimpressed upon the' grids of' the two tubes of the detector l) in par:llel.

'.lhe selected carrier frequency will beat with all three side bands butwill produce 'an intelligible and audible low frequency bandcorresponding only to that side band which was originally modulated bythe carrier selected. 'lhe other side bands will produce frequencieswhich, if the lcarriers are properly chosen, will be above audibilit-y.This renders it unnecessary to provide 'complicated selecting devicessuch aaband filters for selecting` the bands themselves. only filtersnecessary at the snbscribers station are the high-pass filter 59 and thecorresponding lowpass filter 63, inciiided in the circuit 54 leading tothe ordinary subscribers set. lin some instances, the latter filter maybe omitted, especially where an anti-side tone subscriberls is provided,the anti-side tone'circuit preventing the carrier frequencies whichmight be detected by the ordinary telephone transmitter from actuatingthe regular telephone receiver. Even where the filter 63 is provided,both filters 59 and 63 may be economically constructed as they comprisebut one inductance and one capacity for each section, and only afewsections need be provided for each filter. |liliis brings the extraapparatus which it is necessary to provide at the subscribers station inaddition to the regular subscribers set down to a very few andinexpensive elements, to Wit: A loud speaking receiver, a simple motorgenerator or rectifier. two

vacuum tubes for a detector, one simple tuned circuit such as may be.used in an ordinary amateurs set for radio telegraphy, a high-passfilter, a low-pass filter, and the simple network filter shown at 57-58.

None of these elements is expensive and no adjustment is necessary, theonly operation required by the subscriber heilig the setting of theswitch 61 to select the desired frequency.

Even these few elements may bereduced by eliminating the motor generatoror rectifier 54 where the circuit shown in Fig. 3 is employed. lin thisarrangement the carrier 'fre-- quencyselected fromthe power circuit bymeans ot the tuned circuit 52 is impressed through the circui't 62 uponthe output circuit of the detpctor between the filaments and the plates,as indicated, and no direct current is supplied to the tubes, thecarrier frequency itself taking' the place of the di- Bll The

lull

litt) rect current. The side bands will be impressed upon 'the inputcircuit through the transformer serially as before, and the networks 57and 58 will select the detected low frequency currents to operate theloud Speake 56. the high frequency carrier finding a path of lowimpedance through the first shun! condensers of the networks 57 and 58.and the tuning condenser 66. Otherwise, the ,receiving apparatus will beas described in connection with Fig. 2. The operation will. of course,he clear without further discussion.

It will be obvious that the general principles herein disclosed may beembodied in many other organizations widely different form thoseillustrated without departing from the spirit of the invention asdefined in the following claims.

lVha't is claimed is:

l. In a system for transmitting amusement, news and the like, aplurality of sources of intelligence, means to modulate a plurality ofcarrier frequencies in accordance with intelligence from sa'id sourcesto produce modulated side bands, means to impress the umnodulatedcarrier frequencies upon one circuit for transmission to a sub` scribersstation and means to impress the v modulated side bands without thecarriers upon another circuit for transmission to the subscribersstation to beat with the unmodulated carrier frequencies transmittedover said first circuit.

2. In a system for transmitting amusementLnews and the like, a pluralityof sources of intelligence, means to modulate a plurality of carrierfrequencies in accordance with intelligence from said sources to producemodulated side bands, means to impress the unmodulated carrierfrequencies upon one circuit for transmission to a subscribers station,means to impress the modulated side bands without the carriers uponanother circuit for transmission to the subscribers station. and meansat the subscribers station for heating the transmitted side bands with adesired carrier to reproduce signaling currents corresponding to theintelligence by which the carrier was modulated at the transmittingstation.

3. In a system for transmitting amuse ment, news and the like, aplurality of sources ofintelligence, means to modulate a plurality ofcarrier frequencies in accordance with intelligence from said sources toproduce modulated side bands, means to impress the unmodulated carrierfrequencies upon one circuit for transmission to al subscribers station,means to impress the`modulated side bands without the carriers uponanother circuit for transmission to the subscribers station, means atthe subscribers circuit for selecting a desired carrier'frequency to theexclusion of the other ca'rrer .means to modulate carrier frequencies inaccordance with intelligence from said sources,

a power transmission circuit, means to super- -pose upon said powertransmission clrcuit umnodulated carrier frequencies corresponding tothe frequencies modulated by said sources of intelligence fortransmission to a receiving station, a telephone circuit over whichtelephonie communication takes place at ordinary. frequencies, and meansfor selecting modulated side bands corresponding to the several sourcesof intelligence and superposing them without the carriers upon saidtelephone circuit for transmission to said receiving station andcombination thereat with the carrier currents transmitted over sa'idpower circuit.

5. In a system for thetransmission of amusement, news and the like, aplurality of sources of intelligence of different types, meansto'modulate carrier frequencies in accordance with intelligence fromsaid sources, a power transmission circuit leading to a subscribersstation, means to superpose upon sa'id power transmission circuitunmodulated carrier frequencies corresponding to the frequenciesmodulated by said sources of intelligence, a telephone circuit overwhich telephonie communication takes place at ordinary frequenciesleading to said subscribers station, means for selecting modula'ted sidebands corresponding to the several sources of intelligence andsuperposing them without the carriersupon said telephone circuit, andmeans at the subscribers station for heating the transmitted side bandswith a desired carrier to reproduce signaling currents corresponding tothe intelligence by which the carrier was modulated at the transmittingstation.

6. In a system for t-he transmission of amusement, news and the like, aplurality of sources of intelligence of different types, means tomodulate the carrier frequencies in accordance with intelligence fromsaid sources, a power transmission circuit leading` to a subscribersstation. means to superpose upon said power transmission circuitunmodulated carrier frequencies corresponding to the frequenciesmodulated by sa'id sources of intelligence, a telephonie circuit overwhich telephonie communication takes place at ordinary frequenciesleading to said subscribers station, means for selecting modulated sidebands corresponding to the several sources of intelligence andsuperposing them neeavw without the carriers upon Asaid telephonecircuit, means at the subscribers circuit for selecting a desiredcarrier frequency to the exclusion of the other carrier frequencies, andmeans for beating the received side bands with the selected carriervfrequency to reproduce signaling currents corresponding to theintelligence in accordance with which lthe selected carrier is modulatedat the transmittingA station. v

7. ln a signaling system, a power circuit leading to a subscribersstation and a telephone circuit leading` to a subscribers station, aplurality of modulators, a source of alternating power current for saidpower circuit, means to produce and select harmonies of the frequencies'supplied by said power circuit to be used as carrier frequencies, meansto impress said carrier frequencies on said modulators and upon saidpower circuit, means to impress signaling currents rupon saidmodulators, thereby producing modulated side bands and unmodulatedcarrier currents, and means to select the modulated side bands to theexclusion of the carrier frequencies and superpose them upon saidtelephone circuit.

"8. ln a signaling system, a power circuit i leading to a subscribersstation and a telequencies on said modulators and upon said powercircuit, means to impress si naling currents upon'said modulators, therey producing modulated side bands, means to select the modulatedsidebands to the exclusion of the carrier frequencies and superpose themuponsaid telephone circuit, `means -at theA subscribers station forselecting a desired carrier frequency, and means for beating thetransmitted sidebands with a selected car` rier to reproduce signalingcurrents corre spending to the intelligence by which the carrier wasmodulated at -the transmitting,

station.

9. In a signaling system, a power circuit leading to a subs'cribersstation and a telephone circuit-leading to a subscribers station, aplurality of modulators, a source of alternating powervcurrent forsaidpower circuit, ueans. to produce and select harmonies of thefrequencies supplied by said power circuit to be used as carrierfrequencies, means to impress said carrier frequencies on saidmodulatorsand upon said power circuit, means to impre'sssignalingcurrents upon said modulators, thereby producing modulated side bands,means to select the modulated side bands to the exclusion of tbecarrierfrequencies and superpose them upon said telephone circuit, means at thesul)u scribers circuit for selecting a desired carrier frequency to theexclusion of the other carrier frequencies, vand means for beating thereceived side bands with the selected carrier frequency to reproducesignaling currents corresponding to the intelligence in accordance withwhich the selected carrier is modulated at the transmitting station.

l0. lln a signaling system, a transmitting station and a receivingstation, independent transmission circuits interconnecting said stationsand means at the transmitting sta tionfor modulating a plurality ofcarrier frequencies in accordance with signaling currents to producemodulated side bands, means to transmit the unmodulated carrierfrequencies to the receiving station over one of said circuits, andmeans to transmit the modulated side bands exclusive of the carrierfrequencies to said receiving station over the other circuit.

11. fn a signaling system, a transmitting station and a receivingstation, independent transmission circuits interconnecting saidstations, means at the transmitting station for modulating a pluralityof carrier frequencies in accordance with signaling cur' rents .toproduce modulated side bands,

means to transmit the unmodulated carrier frequencies to the receivingstation over one of said circuits, means to transmit 'the modulated sidebands exclusive of the carrier frequencies to said receiving stationover the other circuit, 'and means at the receiving sta-V tion to beatthe side bands transmitted over one of the circuits with a selectedcarrier frequency transmitted over the other circuit to produce a lowfrequency signal corre-V sponding to the signal'byy which the selectedcarrier was modulated atv the transmitting station.

12. In a signaling system, a transmitting station and a receivmgstation, independent transmission circuits interconnecting saidstations, means at the transmitting station' formo'dulating a pluralityof carrier fre-` quencies in accordance with signalin currents toproduce modulated side ldands, means to transmit the unmodulated carrierfrequencies 'to the receiving station over one of said circuits, meanslto transmit the modulated side bands exclusive of the carrier fre-vquencies to said receiving station over the other circuit, means at thereceiving station for selecting any one ofl the carriers trans- 'mittedover the one circuit to the exclusion of the other carrier frequencies,and means for beating the side bands transmitted over the other circuitwith the selected carrier to reproduce the signal in accordance withwhich the selected carrier frequency was modulated at the transmittingstation.

13. In a signaling system, an alternating current power circuit and atelephoneiciidV cuit, means for transmitting modulated ciated with thetelephone circuit, means for supplying ythe operating current for saidduplex vacuum tube detector from said alternating power circuit, a .loudspeaking receiver associated with said detector, and balancedvconnections to thedetector from said power circuit so that iuctuationsin t-he operating current supplied to the detector will balance eachother in the two halves of the duplex detector. i

14. In a signaling system, an alternating current power circuit and atelephone circuit, means for transmiting modulated high frequency bandsover the telephone circuit, a. duplex vacuum tube detector associatedwith the telephone circuit, means for supplying the filament heatingcurrents for said duplex detector from said alternating` power circuit,and a. loud speaking receiver associated with said detector, andbalanced connections to said detector from said power' and beat-ing allof the side bands at the. re-

ceiving station with an alternating wave correspondinor to the carrierfrequency for one of the side bands to the exclusion of wavescorresponding to the carrier frequencies for other side bands to producea signal wave within the telephone range cor responding to one of thesignals only.

16. In a transmission system, the method which consists in modulatingeach of a plurality of carrier frequencies in accordance with differentsignals, suppressing the carrier current components while transmittingside band components to-a receiving station, beating all of the sidebands at the receiving station with an alternating wave correspondin tothe carrier frequency for one ofthe si e bands to the exclusion of wavescorresponding to the carrier frequencies for other the side bands to areceiving station, impressing frequenciescorresponding to the carrierfrequencies upon a common circuit at the receiving station, selectingone of said frequencies to the exclusion of 'the others, and beating thereceived side bands with the selected fiequency to produce a signal wavewithin the telephone range corresponding to one of the original signalsonly.

18. In a transmissionsystem in which the signal is transmitted by meansof a carrier frequency and is reproduced by a detector at the receivingstation, the method which consists in transmitting a plurality of sidebands corresponding to different signals without the correspondingcarrier components, impressing all of the side bands upon the detectorat the receiving station, and simultaneously impressing upon thedetector an alternating wave corresponding to the carrier frequency forone of the side bands to the exclusion of waves corresponding to thecarrier frequencies for other side bands to produce stepped down bandsonly one of which is within the telephonic range.

19. In a transmission system, means for modulating each of a pluralityof carrier frequencies in accordance with separate signals, means tosuppress the carrier frequency components while transmitting the sideband components to a receiving station, means whereby an alternatingwave corresponding to the carrier frequency for each side band may beproduced, and means at the receiving station to beat all of the sidebands with an alternating wave corresponding to the carrier frequency ofone of the sidey bands to the exclusion of waves corresponding to othercarrier frequencies, thereby to produce la signal wave within thetelephone rang'e corresponding to only one of the signals. 1

20. In a transmission system, means for modulating each of a pluralityof carrier frequencies in accordance with separate signals, means tosuppress the carrier frequency 'components while transmitting the sideband components to a receiving station, means whereby an alternatingwave corresponding to the carrier frequency for each side band may beproduced, means at the receiving station to beat all of the side bandswith an alternating wave corresponding to the carrier frequency of oneof the sidr.

ing to other carrier frequencies, thereby to producea signal wave withinthe telephone range corresponding to only one of the signals, and meansto suppress frequencies above the telephone range.

21. In a transmission system, means for modulating each of a pluralityof carrier frequencies in accordance with separate signals, means tosuppress the carrier frequency components while transmitting the bandsto the exclusion of waves correspon"` llO side band components to areceiving station,

a circuit at the receiving station upon which are impressed frequenciescorresponding to each of .the suppressed carriers, means to select fromsaid circuit a frequency corresponding to the carrier of a desiredsignal, and means to beat ali of the 4side bands with the selectedcarrier to produce a signal wave within the telephone rangecorresponding to one of the signals only. A

22. In a transmission system, means to transmitl a plurality of sidebands corresponding to different signals Without transmitting thecorresponding carriers, a' receiving/station.including a detector, meansto impress all of said side bands upon the detector, means whereby analternating Wave corresponding to the carrier frequency foieach sideband may be produced, and means i vto impress upon the detector analternating wave corresponding to one of the suppressed carriers to theexclusion of Waves corresponding to other-carrier frequencies, thereephone range Corresp by to produce a signal wave within the telephonerange corresponding to only one of the side bands.

23. In a transmission system, means to transmit a plurality of sidebands corresponding to diierent signals Without transniitting thecorresponding carriers, a receiv. ing station including a detector,means to impress all of said side bands upon the detector, a circuit atthe receiving station upon which are impressed frequencies correspondingto all of the suppressed carriers, means to select from said circuit afrequency corre` sponding to the carrier of a desired signal and impresssaid frequency upon the detector to produce a. signal wave Within thetelebands only.

In testimony whereof, I have signed my l name to this specification this24th day of February, 1922.

HERMAN A. AFFEL.

onding to one of the side 4,0

